HAI BEN DAVID:

Dayyan, and later gaon in Pumbedita from 890 to 897. He is mentioned in Isaac ibn Ghayyat's "Halakot," in connection with the curious Bagdad custom of reciting the "'Abodah" on the morning of the Day of Atonement, which custom even Hai b. David was unable to abolish. It is probable that he wrote in Hebrew. According to somewhat doubtful Karaitic sources, he wrote an anti-Karaitic book with the purpose of justifying the Rabbinite calendar, the calculation of which is ascribed perhaps by him, if not by Hai ben Sherira, to R. Isaac Nappaḥa (comp. Pinsker, "Liḳḳuṭe Ḳadmoniyyot," pp. 148 et seq.).